JP6094802B2 - Paper cooling device and image forming apparatus having the same - Google Patents

Description

  The present invention relates to a sheet cooling device that cools a sheet while it is transported by an endless belt.

  For example, an electrophotographic image forming apparatus includes a charging device that uniformly charges a photoconductor, an exposure device that exposes the surface of the photoconductor to form an electrostatic latent image, and the electrostatic latent image is visible with toner. The image forming apparatus includes a developing device that forms an image, a transfer device that transfers the toner image on the photosensitive member to the paper, and a fixing device that fixes the toner image on the paper to the paper by heating and pressing. Here, a commonly used fixing device is one in which a sheet is passed through a nip portion of a pair of pressure-contacted rollers and heated and pressed to melt and fix a toner image on the sheet.

  In recent years, image forming apparatuses have been speeded up, and sheets are discharged from the fixing device at high speed. Since the toner image on the paper discharged at high speed has not been sufficiently cooled, the softened wax component on the image may adhere to the paper passing path and cause image noise. In addition, when image formation is performed on both sides of a sheet, a high-temperature sheet is conveyed again to an image forming unit such as a transfer device, so that the temperature of the image forming unit increases and process stability may be impaired.

  Therefore, for example, in Patent Document 1, a heat sink having a plurality of plate-like fins provided in an endless belt at the same time as holding and transporting a sheet by a pair of endless belts on the downstream side of the fixing device in the sheet transport direction. Has proposed a paper cooling device for cooling the paper. As shown in FIG. 6, in the paper cooling apparatus proposed here, the heat sink 73 is arranged so that the formation direction of the plate-like fins 732 and the paper conveyance direction are orthogonal to each other, and one endless belt 71 is arranged. The heat sink 73 is air-cooled by supplying air from the opening toward the other opening by the fan motor 70a.

JP 2009-161347 A

  However, in the proposed paper cooling apparatus, the temperature of the air supplied by the fan motor 70a increases as it flows from one opening of the endless belt 71 toward the other opening, so that the downstream side of the air flow Then, the cooling efficiency is lowered, and noise such as uneven glossiness is generated in the image.

  The present invention has been made in view of such a conventional problem, and an object of the present invention is to provide a sheet cooling apparatus that has high cooling efficiency and can be cooled uniformly in the width direction of the endless belt.

  Another object of the present invention is to provide an image forming apparatus in which image noise such as gloss unevenness does not occur in a toner image on paper and high image quality can be obtained.

The sheet cooling device according to the present invention that achieves the above object includes a first endless belt that conveys a sheet, a flat plate-like base that is in contact with an inner circumferential surface of the first endless belt, and the base. A heat dissipating member having a plurality of plate-like fins substantially parallel to the paper transport direction on the other surface side thereof, a pressing member pressing the paper transported by the first endless belt against the heat dissipating member side, and the heat dissipating member And air blowing means for applying an air flow from the downstream side to the upstream side in the paper conveyance direction.

  Here, an air supply port and an exhaust port are formed and a housing that covers the heat radiating member is further provided, the air supply port is formed downstream of the heat radiating member in the paper transport direction, and the air exhaust port is formed from the heat radiating member. May also be formed on the upstream side in the paper conveyance direction.

  Alternatively, the air blowing means may be provided downstream of the heat radiating member in the paper conveyance direction and inside the first endless belt, and a plurality of holes may be formed in the first endless belt.

The plurality of plate-like fins are preferably formed substantially perpendicular to the base and at a predetermined interval .

  Further, a first rectifying plate that distributes the air flow may be further provided so that the flow rate of air flowing between the plate-like fins is uniform on the downstream side of the heat dissipation member in the paper conveyance direction.

  A second rectifying plate that guides and discharges the air flowing between the plate-like fins in the width direction of the first endless belt may be further provided on the upstream side of the heat dissipation member in the paper conveyance direction. .

  It is preferable to further provide a second endless belt in which the pressing member is disposed on the inner peripheral surface thereof.

  According to the present invention, in the image forming apparatus having a fixing unit that heats and fixes the toner image transferred to the sheet to the sheet, the image forming apparatus is provided at any one of the above positions downstream of the fixing unit in the sheet conveying direction. An image forming apparatus provided with the sheet cooling device described above is provided.

  In the sheet cooling device of the present invention, the air flow from the downstream side in the sheet conveying direction to the upstream side is applied to the heat radiating member by the blower, so the air having the lowest temperature is applied at the position where the sheet temperature is the lowest. As a result, high cooling efficiency can be obtained. Further, the endless belt can be cooled without temperature unevenness in the width direction.

  In the image forming apparatus of the present invention, since the paper cooling device is provided on the downstream side of the fixing device in the paper transport direction, the paper that has passed through the fixing device is quickly cooled, and the toner image on the paper is glossy. High image quality can be obtained without image noise such as unevenness.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus equipped with a sheet cooling device of the present invention. It is a horizontal sectional view showing a paper cooling device of the present invention. It is a vertical sectional view showing a paper cooling device of the present invention. It is a perspective view which shows the paper cooling device of this invention. It is a perspective view which shows other embodiment of the paper cooling device of this invention. It is a perspective view which shows the conventional paper cooling device.

  Hereinafter, the sheet cooling device and the image forming apparatus according to the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments.

  FIG. 1 is a schematic configuration diagram showing an embodiment of a sheet cooling device and an image forming apparatus according to the present invention. An image forming apparatus 8 shown in FIG. 1 includes a printer unit 81 that forms an image, an image reader unit 82 that reads a document image, and an operation display unit 83 that allows a user to input image forming conditions and display the state of the apparatus. With. The image reader unit 82 is a known unit that reads a document placed on a document glass plate (not shown) by moving a scanner, and obtains image data converted into an electrical signal by a CCD image sensor (not shown). It is done.

  The printer unit 81 carries a toner image, and a charging device 2 that uniformly charges the surface of the photosensitive member D around the cylindrical photosensitive member D that rotates clockwise, and light on the surface of the photosensitive member D. An exposure device 3 that forms an electrostatic latent image by irradiation, a developing device 4 that supplies toner to the photoconductor D and develops the electrostatic latent image on the photoconductor D to form a toner image, and a developing device 4 A transfer roller 5 for transferring the formed toner image on the photoconductor D to the paper P, and a cleaning device 6 for removing toner remaining on the photoconductor D without being transferred to the paper P are provided.

  The charging device 2 is a scorotron charging device, and includes a box-shaped shield electrode 22 having an opening on the side facing the photoreceptor D, a discharge electrode 21 stretched in the shield electrode 22, and a shield electrode 22. And a grid electrode 23 attached to the opening. When a voltage of several kV is applied to the discharge electrode 21, a corona discharge is generated, and the surface of the photoreceptor D is uniformly charged. The type of the charging device 2 is not particularly limited. Of course, a roller-type charging member, a blade-shaped charging member, a brush-shaped charging member, or the like may be used.

  The exposure device 3 performs exposure by selectively irradiating light on the surface of the photoreceptor D uniformly charged by the charging device 2 based on image data input from an external device such as a personal computer, A predetermined electrostatic latent image is formed on the surface of the photoreceptor D.

  The developing device 4 includes a housing 41, a developing roller 42 that is rotatably provided facing the photoreceptor D, and a transport roller 43 that transports the developer toward the developing roller 42. In the housing 41, a developer composed of toner and a carrier (both not shown) is accommodated. When a developing bias voltage is applied to the developing roller 42, the toner moves to the photosensitive member D due to the potential difference between the voltage applied to the developing roller 42 and the electrostatic latent image on the photosensitive member D, and the electrostatic latent image on the photosensitive member D is transferred. Is visualized (toner image) with toner.

  The transfer roller 5 is rotatably provided by a drive motor (not shown) connected to the transfer roller 5 and is pressed against the photoreceptor D by a biasing member (not shown). In addition, a voltage having a polarity opposite to the toner charging polarity is applied to the transfer roller 5 by a voltage applying unit (not shown). When the paper P passes between the photoconductor D and the transfer roller 5, the voltage is applied to the transfer roller 5, and the toner image formed on the photoconductor D is transferred to the paper P.

  The cleaning device 6 includes a cleaning blade 61 that presses against the photoconductor D, and removes untransferred toner remaining on the surface of the photoconductor D from the photoconductor D.

  Under the printer unit 81, a paper feed cassette 51 that stores paper P is detachably disposed with respect to the printer unit 81. The paper P stored in the paper feed cassette 51 is sent to the transport path 50 one by one in order from the uppermost paper by the rotation of the paper feed roller 52 disposed on the upper side of the paper feed cassette 51. The paper P sent out from the paper feed cassette 51 is conveyed to the registration roller pair 53 and sent out from the registration roller pair 53 to the nip portion between the transfer roller 5 and the photoconductor D in synchronization with the rotation of the photoconductor D. As described above, the toner image is transferred onto the paper P.

  Further, the printer unit 81 includes a fixing device 1 that fixes the toner image transferred from the photoreceptor D to the paper P. The fixing device 1 includes a fixing roller 11 including a halogen heater H and a pressure roller 12 that is in pressure contact with the fixing roller 11. When the paper P passes through the nip portion between the fixing roller 11 and the pressure roller 12, the toner image is melted and fixed on the paper P by being heated and pressurized. The paper P is discharged from the discharge port 55 to the paper discharge tray 85 on the side of the main body through the paper cooling device 7a. The sheet cooling device 7a will be described later.

  The image forming apparatus 8 includes a control device 84 that comprehensively controls components related to the image forming device 8. The control device 84 includes the photosensitive member D, the developing roller 42, the transfer roller 5, and a paper feed roller. 52, the rotation driving of the conveying roller 53 and the fixing roller 11, and the operation of the charging device 2, the exposure device 3, the developing device 4, the halogen heater H, and the like are controlled. Of course, the control operation of the control device 84 is executed according to the setting condition input by the user from the operation display unit 83.

  In the above-described embodiment, the sheet cooling device 7 is built in the image forming apparatus 8. However, the sheet cooling device 7 may be arranged side by side in the main body of the image forming apparatus as an independent device.

  2 is a front vertical sectional view of the sheet cooling device 7a, FIG. 3 is a horizontal sectional view, and FIG. 4 is a perspective view. In the sheet cooling device 7a shown in these drawings, an endless belt 71 and an endless belt 72 are respectively hung on four rollers 78a to 78d and four rollers 79a to 78d, and a roller 78a, a roller 79a, and a roller 78b. The roller 79b is in pressure contact with the endless belts 71 and 72 therebetween. The endless belt 71 is provided with a heat sink (heat radiating member) 73 so as to contact the inner peripheral surface of the endless belt 71. Then, five pressing rollers (pressing members) 75 are in pressure contact with the heat sink 73 with the endless belt 71 and the endless belt 72 sandwiched between them by an unillustrated biasing means. Thereby, the endless belt 71 and the endless belt 72 are pressed against the heat sink side.

  The heat sink 73 has a flat plate-like base portion 731 and a plurality of plate-like fins 732 provided at a predetermined interval with respect to the base portion 731, and the back surface of the base portion 731 is in contact with the endless belt 72. Yes. The formation direction of the fins 732 is parallel to the paper transport direction. A housing 74 is provided so as to cover the heat sink 73.

  As shown in FIG. 3, the housing 74 has an air supply port 741 downstream of the heat sink 73 in the paper transport direction, and an exhaust port 742 upstream of the heat sink 73 in the paper transport direction. A blower fan (blower unit) 70 is provided near the outside of the air supply port 741 of the housing 74. Further, a first rectifying plate 76 that distributes the air flow so that the air supplied from the air supply port 741 flows equally between the fins 732 is provided on the downstream side of the heat sink 73 in the housing 74 in the paper conveyance direction. ing. A second rectifying plate 77 is provided on the upstream side of the heat sink 73 in the housing 74 in the paper conveyance direction to guide the airflow flowing between the fins 732 to the discharge port 742.

  The paper P conveyed to the paper cooling device 7a is nipped and conveyed between the endless belts 71 and 72. During this time, the paper P is pressed against the heat sink 73 together with the endless belts 71 and 72 by the pressing roller 75, and the heat of the paper P is transmitted to the heat sink 73 via the endless belt 71. Thereby, the paper P is cooled and sent out from the paper cooling device 7a.

  On the other hand, the air supplied by the blower fan 70 is sent into the housing 74 from the air supply port 741, passes through between the fins 732, and is discharged from the discharge port 742. The heat released from the base 731 and the fins 732 of the heat sink 73 is absorbed by the air flow by the blower fan 70. What is important here is that air flows from the downstream side in the paper conveyance direction toward the upstream side with respect to the heat sink 73.

The amount of heat Q transferred from the paper P to the air flow is expressed by the following equation.
Moving heat quantity Q = (paper temperature−air flow temperature) / thermal resistance In the equation, the thermal resistance represents the difficulty of heat transfer of the paper cooling device, and the smaller the thermal resistance, the larger the moving heat quantity. If the thermal resistance is the same, the amount of heat transferred increases as the difference between the sheet temperature and the air flow temperature increases.

  If the direction of the air flow is a direction perpendicular to the paper conveyance direction as in the conventional case, the temperature of the air flow is higher on the downstream side of the air flow in the heat sink 73 (one side in the width direction of the endless belt). The difference from the paper temperature is reduced and the cooling efficiency is lowered. For this reason, a difference occurs in the cooling efficiency in the width direction of the endless belt 71. On the other hand, in the cooling device of the present invention, the direction of air flow is from the downstream side to the upstream side in the paper conveyance direction, so the air flow temperature in the width direction of the endless belt 71 is substantially equal, and there is no difference in cooling efficiency. Does not occur. In addition, the intake side where the airflow temperature is low is the downstream side in the paper conveyance direction where the paper temperature is low, and the exhaust side where the airflow temperature is high is the upstream side in the paper conveyance direction where the paper temperature is high. Efficiency is obtained.

  Further, since the air fed into the housing 74 from the air supply port 741 is equally distributed between the fins 732 by the first rectifying plate 76, the air flow rate in the width direction of the endless belt 71 becomes substantially equal. The cooling efficiency in the direction is substantially the same. And since the air which passed between each fin 732 is guide | induced to the discharge port 742 by the 2nd baffle plate 77 and discharged | emitted, while the pressure loss of an airflow is suppressed and the housing 42 grade | etc., Is unnecessary by the temperature rising air It is suppressed that it is warmed.

  The material of the endless belts 71 and 72 is not particularly limited as long as it has excellent thermal conductivity, but a polyimide film, a nickel electroformed film, a polyethylene film, or the like is preferable. Moreover, as a ventilation means, conventionally well-known things, such as an axial fan and a centrifugal fan, can be used.

  FIG. 5 shows another embodiment of the sheet cooling apparatus according to the present invention. The sheet cooling device 7b shown in this figure is different from the sheet cooling device 7a of the above-described embodiment in that five fan motors (blowers) in the width direction are provided downstream of the heat sink 73 in the endless belt 71a in the sheet conveyance direction. ) 70a are arranged side by side, and a housing is not provided, but instead an endless belt 71a in which a plurality of holes 711 are formed is used. The air supplied from the fan motor 70a flows between the fins 732 in parallel with the paper conveyance direction from the downstream side in the paper conveyance direction to the upstream side, and is discharged to the outside from the plurality of holes 711 formed in the endless belt 71a. Is done. Even with this configuration, the same effect as that of the sheet cooling device 7a can be obtained by the sheet cooling device 7b.

Using the image forming apparatus shown in FIG. 1, paper fixing was performed under the following conditions, and the paper temperature after fixing was measured and found to be 110.degree.
Environmental temperature: 25 ° C
Fixing temperature: about 200 ° C
Paper basis weight: 128 g / m ²
Paper transport speed: 400mm / sec

Example 1
In the image forming apparatus shown in FIG. 1, when the temperature of the sheet that passed through the sheet cooling apparatus was measured by driving the sheet cooling apparatus, it was 54 ° C. and the temperature unevenness in the width direction was 1 to 2 ° C.

(Comparative Example 1)
In the image forming apparatus shown in FIG. 1, the conventional paper cooling device shown in FIG. 6 is attached, and the temperature of the paper is measured in the same manner as in Example 1. The temperature unevenness in the width direction is 2 to 3 ° C. there were.

  In the sheet cooling device of the present invention, the air flow from the downstream side in the sheet conveying direction to the upstream side is applied to the heat radiating member by the blower, so the air having the lowest temperature is applied at the position where the sheet temperature is the lowest. As a result, high cooling efficiency can be obtained. Further, the endless belt can be cooled without temperature unevenness in the width direction, which is useful.

7a, 7b Paper cooling device P Paper 70 Blower (blower)
70a Fan motor (air blowing means)
71, 71a Endless belt (first endless belt)
72 Endless belt (second endless belt)
73 heat sink 74 housing 75 pressure roller (pressing member)
76 1st rectifier plate 77 2nd rectifier plate 711 hole 741 air supply port 742 exhaust port

Claims (8)

A first endless belt for conveying paper;
A flat base that is in contact with the inner peripheral surface of the first endless belt and one surface, and a heat dissipating member that includes a plurality of plate-like fins substantially parallel to the paper transport direction on the other surface of the base ;
A pressing member that presses the sheet conveyed by the first endless belt against the heat radiating member;
A sheet cooling apparatus comprising: a blowing unit that applies an air flow from the downstream side in the sheet conveyance direction to the upstream side with respect to the heat radiating member. An air supply port and an exhaust port are formed, and further includes a housing covering the heat dissipation member;
The sheet cooling device according to claim 1, wherein the air supply port is formed downstream of the heat radiating member in the paper transport direction, and the exhaust port is formed upstream of the heat radiating member in the paper transport direction.   2. The paper according to claim 1, wherein the blower is provided downstream of the heat radiating member in the paper conveyance direction and inside the first endless belt, and a plurality of holes are formed in the first endless belt. Cooling system. The sheet cooling device according to any one of claims 1 to 3, wherein the plurality of plate-like fins are formed substantially perpendicular to the base and at a predetermined interval . 5. The first rectifying plate that distributes the air flow so that the flow rate of air flowing between each of the plate-like fins is uniform on the downstream side of the heat dissipation member in the paper conveyance direction . The paper cooling device according to any one of the above. In the conveyance direction upstream side of the heat radiating member, according to claim 1, further comprising a second rectifying plate for discharging guide the air which has flowed between each of said plate-like fins in the width direction of the first endless belt The paper cooling device in any one of -5 .   The sheet cooling device according to any one of claims 1 to 6, further comprising a second endless belt in which the pressing member is disposed on an inner peripheral surface thereof. In an image forming apparatus having a fixing unit that heats and fixes a toner image transferred to a sheet to the sheet,
8. An image forming apparatus comprising: the sheet cooling device according to claim 1 provided downstream of the fixing unit in a sheet conveyance direction.